I don't understand why elevation data is not stored in the sample using a standard length unit. Why is it stored in HKQuantityTypeIdentifier.flightsClimbed (which is 10 feet)? Surely it is not a memory usage issue. Treadmill GATT provides elevation in meters. Using HKMetadataKeyElevationAscended for the total elevation gain throws away a lot of data. Why is there no support for weighted vest or backpack? Changing body weight is not the same and provides incorrect energy. Users want to compare workouts with different weights. I don't see any metadata key for carried weight.

There are many units which are inverse of standard units, e.g. wave period vs Hz, pace vs speed, Siemens vs Ohms, ... Dimension can be subclassed to create the custom units. How to extend Measurement.converted( to: )? I was looking at somehow using UnitConverter and subclass to something like UnitConverterInverse. Thoughts?

When I used to do Migrations, I always used ETL and then push to a dev system to review/test before going production. The migration support is SwiftData is fine for a little tweak. I might as well just just use new schema and context and write the custom code than use the SwiftData migration support.